Heating power of a candle

A timetable clash means your next chemistry lesson has to be in a classroom. Your teacher says you won’t be able to do practical work as you won’t be able to use Bunsen burners. Find the number of candles which have the heating power of one Bunsen burner.

This experiment should take 50–70 minutes depending on ability

Equipment

• Eye protection should be worn when heating liquids.
• Accurate balances should be available.
• Candle
• Thermometer
• Small metal cans
• Glass beakers, 100 cm³
• Measuring cylinder, 10 & 50 cm³
• Stop clock
• Bunsen burner
• Tripod
• Gauze
• Heatproof mat
• Clamp stand

Health, safety and technical notes 

• Read our standard health and safety guidance here.
• Wear eye protection. 
• Hot candle wax can burn, and stain clothes. Wear lab coats or aprons if desired. 
• This is an open-ended problem-solving activity, so the guidance given here is necessarily incomplete.

Possible approaches

Students should compare the effect of heating the same amounts of water, using a candle and a Bunsen burner, over the same time period, e.g. 2, 5 or 10 minutes.

Many groups fail to appreciate that it is the temperature change that is important, i.e. they try to find an answer simply by comparing final temperatures.

Other factors may be considered, such as the suitability of different heat sources, e.g. sooty candle flame. 

Possible extension 

The experiment indicates to students the number of candles equivalent to a Bunsen burner.

A simple extension of this would be to devise an experiment to test that hypothesis. (The results from one school suggest that 2 candles = 1 Bunsen burner.

If this is true, why don’t all schools use candles?) 

Notes

Large pieces of wick cause very large flames (this requires careful supervision of the ‘bright sparks’)

Ensure that the activity takes place well away from any flammable or combustible substances.

Eye protection should be worn when heating liquids.